A semiconductor device array contains individual integrated circuits or semiconductor packages. Connectors 105 of the semiconductor packages are exposed at the top of the semiconductor array 100, as illustrated in FIG. 1A. The connectors 105 are typically made of copper. To prevent oxidation on the copper surface, the connectors 105 are plated with a lead finished material, such as matte tin (Sn), using electroplating. As a result, the top surfaces of the connectors 105′ are thereafter tin plated, as illustrated in FIG. 1B.
Singulation is a process of separating each semiconductor package from a molded sheet. Dicing or sawing is a process that singulates the semiconductor array 100′ into individual or singulated semiconductor packages. Conventionally, the electroplated semiconductor array 100′ is diced into singulated semiconductor packages to be shipped to customers for assembly onto printed circuit boards. FIG. 1C illustrates a saw 115 dicing the semiconductor array 100′. The saw 115 typically follows a saw path 110 across the plated connectors 105′, resulting in connectors on peripheral edges of the singulated semiconductor packages.
FIG. 2A illustrates a singulated semiconductor package 200 having a plurality of connectors 205 on the peripheral edges. Although tops of the connectors 205a are tin plated, sidewalls of the connectors 205b are exposed (e.g., without tin plating), because the dicing occurred after the semiconductor array 100 was electroplated with the lead finished material. If the singulated semiconductor package 200 is stored in inappropriate environments and/or conditions (e.g., moisture in the air, acids, bases, salts, oils, aggressive metal polished, and other solid and liquid chemicals) after singulation, then the exposed surfaces 205b become sites for potential corrosion 210 such as copper oxide, as illustrated in FIG. 2B. This aging process is known as oxidation. The exposed surfaces 205b, usually deposited with pollutant layers of oxide and other nonmetallic compound 210, often interfere with or inhibit solder wettability. The resulting oxide layer reduces solderability because contamination 210 prevents the metal from soldering well. The rate of oxidation can increase with an increase in temperature or humidity. Solder problems are a common cause for device failures.
A perfectly clean surface is required for assembly of singulated semiconductor packages 200 onto printed circuit boards. Since metal oxides form a barrier that prevents molten solder from forming a true metallurgical bond, the metal oxides must be removed prior to soldering or must be avoided in the first place.
The present invention addresses at least these limitations in the prior art.